Method of and system for measuring the state of charge or discharge of secondary batteries



Y June 6,1

METHOD OF AND SYSTEM FOE MEASURING THE STATE OF CHARGE 0R DISCHARGE OF SECONDARY BATTERIES EiledOct. 30, 1936 In ven for Erich Wc''e Patented June e, 1939 PATENT oI-FicE RIETI-10D 0F AND SYSTEM FOB MEASURING `V THE STATE F CHARGE 0R DISCHARGE 0F SECONDARY BATTERIES Erich Witte, Hagen, Germany, assignor to Accumnlatoren-Fabrlk Aktiengesellschaft, 13er-- lin, Germany, a joint stock company of Ger- Application October 30, 1936, Serial No. 108,477 In Germany October 31, 1935 2Claims.

My invention relates to improvements in the method of and system for measuring the state of charge or discharge of secondary batteries, and more particularly in the method and system 5 in which the said state of charge or discharge is determined by measuring the terminal voltage of the battery by a circuit arrangement including a`voltmeter and a circuit for compensating for the variations in the terminal voltage, caused by the apparent internal resistance of the battery, from the theoretical E. M. F. of the battery when the current value is zero, the said circuit being connected to the system in such a way that besides the normal voltage measuring current also a part of the charging or discharging current iiows through the voltmeter coil, so that the voltmeter indicates a voltage value, which on the discharge of the battery is higher than the actual voltage applied by the battery to the terminals of the voltmeter, and is higher by as much as the voltage drop caused by the apparent internal resistance in the battery. Systems of this type are shown and described in British Patent 438,407. As has been described in this patent, a variable control resistance through which a part of the charging or discharging current passes, is connected with the measuring instrument, and the said resistance is adjusted in dependence on the apparent internal resistance and the size of the battery. However, by vvarying the current through the resistancev the value of the resistance of the measuring instrument and therewith its constant is varied.

The object of the improvements is to obviate 35 this disadvantage, and with this objtct in view the current through a control resistance in parallel and/or that through a resistance in series with the measuring instrument is sc adjusted that the current through the measuring instrument remains constant while the apparent internal resistance of the battery varies. Thus the measuring instnirnent gives the same deflection so long as the capacity oi the battery remains at about the same value. As the apparent internal resistance oi' the battery increases, the current in the control resistance which is in parallel with the measuring instrument must be increased, and that in the resistance which is in series with the instrumentlmust be reduced by the same amount. By this adjustment the current in the measuring instrument remains constant, whereas ii the adjustment were not made the current through the measuring instru- 55 ment would/ fall and even it the capacity re- (c1. irs-183) mained the same, different readings would be v obtained.

For the'purpose oi.' explaining the invention several examples embodying the same have been shown in the accompanying drawing in which the same reference characters have been used in all the views to indicate corresponding parts. In said drawing,

Fig. l is a diagram showing the circuit of my improved system, and

Figs. 2 and 3 are similar showing modifications.

Referring to Fig. 1 a variable resistance r is connected in series with the coil of a measuring instrument s for showing the state oi' charge or discharge of a battery B. A control resistance v, which is also variable, is shunted from a diverting resistance w and connected in parallel with the coil of the said measuring instrument s. The resistances v, 1' are preferably adjusted simultaneously. For this purpose the adjusting means of v and r are mechanically coupled together, as is indicated by an arrow extending across both resistances, so that for each value oi v there is a corresponding denite value oi' r. Thus, by properly regulating the current iiow through the resistances v and r, the current in the coil of the said measuring `instrument s and the deflection of the instrument are kept constant as the apparent internal resistance of the battery B varies..

The control resistance v may, in certain cases, be kept constant (although the effective value of the resistance is adjusted). This is shown in Fig. 2. One end o! the constant resistance v is connected to the choke diverting resistance w, while the other end is connected as in a potentiometer toa variable point in the resistance 1', adjusted according to the compensation required. 'I'his is suilicient to fulll the requirements set forth above. In order to obtain practical equality or the voltage constant to the desired degree o! accuracy, with varying degrees of compensation a fur-ther resistance p (Fig. 3) is connected across the diverting resistance w.` 'I'he voltage necessary for compensation is taken on the resistance p at the variable point ot connection thereto of one end of the selected xed resistance 17. By suitably choosing `the potentiometer resistance p practical equality of the voltage constant of the circuitis attained to any desired extent while the degree of compensation is varied.

I claim:

1. The herein described system for measuring the state of charge and discharge of an electric storage battery, that includes, in combination with the battery and its charging and dischargl ing circuit, a measuring circuit connected to the terminals of the battery and including, arranged in series, a voltmeter and a resistance, and a circuit adapted to make compensation in the measuring circuit for variations in the apparent internal resistance of the battery, which compensating circuit includes-a diverting resistance arranged in series with the charging and discharging circuit and a resistance thattogether with the voltmeter is arranged in shunt with said diverting resistance; the improvement herein described which consists in an auxiliary resistance Within the compensating circuit bridging the leads to and fromthe diverting, resistance, and a movable contact that brings a larger or smaller portion of said auxiliary resistance into circuit with the resistance associated with the diverting resistance in said compensating circuit.

2. In the method of ascertaining the state of charge and discharge of a battery that consists in measuring, with a meter in a measuring circuit connected across the terminals of the battery, the terminal Voltage of the battery compensated by a value depending on a current d1- verted from the charging and discharging circuit of the battery and flowing in a compensating circuit connected in shunt with-the meter in said measuring circuit; the renement herein described which consists in establishing, by correlatively adjusting the eiective values of resistances in said circuits, such electrical balance of the compensating and measuring circuits that the current in said compensating circuit is automatically varied in accordance with variation in the apparent internal resistance of the battery while the current in said measuring circuit is automatically varied .in accordance with the changes in terminal voltage, with compensation for the change in the value of such measuring current caused by, or accompanying, variation in value of the current flowing in said compensating circuit, whereby, for a given state of charge and discharge of thebattery, the indication of said meter will be the same irrespective of the apparent internal resistance of the battery and the value of the current in said charging and discharging circuit.

ERICH WITTE. 

